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Hirst, Alastair, Bott, Nathan and Lee, Randall 2013, Plankton survey of Asterias amurensis larvae in coastal waters of : final report. Fisheries Victoria Technical Report, Department of Primary Industries, Queenscliff, Vic..

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Plankton survey of Asterias amurensis larvae in coastal waters of Victoria (August ‐ September 2012)

Final Report Alastair Hirst1, Nathan Bott2, and Randall Lee3

1 Fisheries Victoria, Department of Primary Industries

2 SARDI Aquatic Sciences, South Australia

3 Environment Protect Authority

April 2013 Fisheries Victoria Department of Primary Industries

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ISSN 1835‐4785

ISBN 978‐1‐74326‐421‐8 (Print)

Survey of Asterias larvae ii

Executive Summary

This report was commissioned to investigate the flowing across Bass Strait incidence of northern Pacific seastar (Asterias to the north coast of Tasmania and returning to amurensis) larvae in Victorian coastal waters, the Victorian coast off Point Hicks as part of a following the discovery of adult seastars at San gyre that dominates central Bass Strait. Remo () in September 2011 and in Asterias larvae were also detected in Western the Tidal River estuary (Wilsons Promontory Port, Andersons Inlet and Tidal River during National Park) in May 2012. this survey. The most likely source of larvae in This study used a combination of plankton these bays and inlets is the intrusion of larvae surveys and hydrodynamic modelling to from the open coast. Whilst there is good examine the distribution of Asterias larvae in evidence that adult populations of seastars have coastal waters between Bay (PPB) been eradicated from Andersons Inlet and Tidal and Port Welshpool in eastern Victoria. River estuary, the presence of adult seastars in Western Port can neither be confirmed nor  Zooplankton assemblages were sampled dismissed based on the results of this survey. during August ‐ September 2012 using a 90 This is because the Asterias larvae detected in μm mesh plankton net. The quantity of Western Port may have either arrived from PPB Asterias DNA (larvae) in plankton samples or originated from a source population within was measured using a genetic probe Western Port. Asterias larvae may also be  The behaviour of Asterias larvae in coastal present in Shallow Inlet, but this location was waters between PPB and Cape Liptrap was not surveyed during this study. modelled using hydrodynamic and Overall the pattern of Asterias incursions at dispersion models. Andersons Inlet, Western Port and Tidal River Asterias larvae were detected in coastal waters appears consistent with natural range expansion between PPB and Wilsons Promontory during via larval dispersal; with PPB as the main source August ‐ September 2012. This finding is of larvae in the region. supported by hydrodynamic modelling of Managers will need to be vigilant to prevent the buoyant particles simulating the behaviour of spread of Asterias along the coastline between Asterias larvae exported from PPB. The PPB and Wilsons Promontory. The presence of hydrodynamic and dispersion model estimated larvae in coastal waters between PPB and larvae could reach the coast off Tidal River in Wilsons Promontory indicates further incursions approximately 44 days, well within the larval are likely in Western Port, Andersons Inlet, duration of 79–112 days for Asterias. around Wilsons Promontory, but also possibly Asterias larvae were not detected in coastal in systems where Asterias has not previously waters east of Wilsons Prom (i.e. been recorded (e.g. Shallow Inlet). Protected and Port Welshpool) during August ‐ September embayments such as Waratah Bay may also be 2012. As no major currents connect the west and susceptible, given the presence of larvae at east coasts of Wilsons Promontory, the absence relatively high levels in this region. of larvae along this coastline is consistent with We recommend further sampling along the west the influence of the prevailing currents in Bass coast of Victoria between PPB and Cape Otway, Strait and their role in transporting Asterias and further east along the East coast larvae. to confirm the outputs of the modelling and the Currents in Bass Strait are primarily influenced pattern of larval dispersal described in this by the prevailing wind direction (SW) and tides. report. Sampling should also be undertaken in Prevailing currents in Bass Strait flow Shallow Inlet, to confirm the presence/absence of principally eastwards, diverging south at larvae in this system.

Survey of Asterias larvae iii

Table of Contents

Executive Summary ...... iii

Introduction ...... 1 Aim of this study ...... 1 This report ...... 2

Methods ...... 3 Plankton sampling ...... 3 Hydrodynamic modelling ...... 3

Results ...... 7 Plankton sampling ...... 7 Hydrodynamic modelling ...... 7

Discussion ...... 11 Distribution of Asterias larvae ...... 11 Role of larval dispersal in causing new outbreaks of Asterias? ...... 12 Could the geographical pattern of Asterias outbreaks in Victoria be explained by other vectors? ...... 13 Conclusions ...... 13

Acknowledgements ...... 15

References ...... 16

Survey of Asterias larvae iv

List of Tables Table 1. Locations sampled in this survey including map codes used in figure 1, date and geographical position……………………………………………………………………………………………………. 5 Table 2. Genetic assay results showing the presence and quantity of Asterias DNA (pg/5 min tow) in each plankton sample...... 8

List of Figures Figure 1. Map of sample locations (for location codes see Table 1)...... 6 Figure 2. Bubble plot showing the quantity of Asterias DNA (pg/ 5 minute plankton tow) recorded at each location between PPB and Port Welshpool...... 9 Figure 3. 200 day simulation of continuous larval release (total of 96000 particles) from Port Phillip Bay between July and November shown as cumulative counts of visits per cell. The dispersion model provides an indication of the likelihood of Asterias larvae presence and key pathways...... 10 Figure 4. Directionally average currents for Bass Strait displaying residual velocity vectors (m/s). Source: SEA (south‐east Australia) hydrodynamic model (Greer et al. 2008) ...... 11

Survey of Asterias larvae v

Introduction

The northern Pacific seastar (Asterias amurensis) 112 days (Bruce et al. 1995). Hydrodynamic is an introduced marine pest currently listed on modelling indicates Asterias larvae may be the CIMPE (Consultative Committee on dispersed over relatively large distances by Introduced Marine Pest Emergencies) trigger list oceanographic processes in south‐eastern (Murphy and Paini 2010). The seastar is native to Australia (Dunstan and Bax 2007). the north‐west Pacific and is likely to have been Although larval dispersal has been implicated in first introduced to south‐east Tasmania from the establishment of Asterias populations along central Japan via ballast water in the 1980s both the Victorian and Tasmanian coasts (Bax (Buttermore et al. 1994, Ward and Andrew and Dunstan 2004, Holliday 2005); no previous 1995). Genetic evidence indicates Asterias was surveys of Asterias larvae have been undertaken subsequently introduced into Port Phillip Bay outside of Port Phillip Bay or the Derwent River (PPB) from the south‐east Tasmania in the mid‐ estuary. This is despite predictions from 1990s, most likely also by ballast water (Murphy hydrodynamic modelling that Asterias larvae are and Evans 1998). likely to occur in Bass Strait (Dunstan and Bax Asterias populations in Australia are primarily 2007). restricted to the south‐east coast of Tasmania, Information on the distribution on Asterias particularly the Derwent River estuary, and larvae in coastal waters is likely to be important PPB. In Victoria adult seastar have also been in identifying the link between larval dispersal recorded at Andersons Inlet in 2003, and more and establishment of new Asterias populations recently at San Remo (Western Port) in along the Victorian coastline; and the role of September 2011 and in the Tidal River estuary, other potential vectors (e.g. ballast water or the (Wilsons Promontory National Park), in May physical translocation of non‐larvae). 2012. Follow up removal efforts and monitoring at all three locations indicates that no viable spawning population survived beyond the year Aim of this study of first detection. It is unclear whether these Following the discovery of Asterias individuals outbreaks represent a natural range extension of at San Remo and in Tidal River estuary, the the population in Victoria facilitated by Department of Sustainability and Environment planktonic larval dispersal or are the product of (DSE) commissioned the Department of Primary physical translocation of non‐larvae (juveniles Industries (DPI) to investigate the incidence of and adults). Asterias larvae in selected coastal waters in August ‐ September 2012. Parks Victoria (PV) The initial introduction of Asterias into also commissioned DPI to survey the Tidal River Australian coastal waters has been linked to the estuary during August ‐ September 2012. capacity of its planktonic larvae to remain viable in ballast water for sustained periods (Ward and The aim of this study was to survey the Andrew 1995). Asterias possess long‐lived following regions/locations for the presence and planktotrophic (feeding) larvae that are capable abundance of Asterias larvae: of remaining in the water column for up to 120  Port Phillip Bay (PPB) days prior to settlement (Bruce et al. 1995).  Western Port (WP) Asterias spawn small eggs, approximately 150  coastal waters between PPB and WP μm long, that hatch and develop through a  coastal waters offshore of Walkerville (South series of stages (gastrula, bipinnaria, Gippsland) and Tidal River, Wilsons brachiolaria) before settling out of the plankton Promontory National Park and metamorphosing into juvenile seastar.  Corner Inlet Adult Asterias spawn during the winter months  coastal waters adjacent to Barry Beach and fertilization of eggs and sperm occurs Marine Terminal and Port Welshpool externally in seawater (Byrne et al. 1997). Larval  Andersons Inlet, and development is strongly temperature dependent  Tidal River estuary and at 12°C (typical of Bass Strait in winter) Port Phillip Bay, Western Port and the South larval duration is estimated to range from 79– Gippsland coast are connected by prevailing

Survey of Asterias larvae 1

currents (Greer et al. 2008), whereas the ports of Port Welshpool and Barry Beach Marine Terminal in Corner Inlet experience high vessel traffic. A genetic probe developed by SARDI aquatic sciences (Bott et al. 2010) was used to measure the quantity of Asterias DNA in zooplankton samples. This approach is the only reliable method of identifying Asterias larvae collected in plankton samples (Bruce et al. 1995, Deagle et al. 2003). This report  Presents the results of Asterias larval surveys undertaken in August ‐ September 2012  Presents the results of hydrodynamic modelling simulating the behaviour of Asterias larvae in Bass Strait  Discusses the role of larval dispersal in the establishment of new populations of Asterias along the Victorian coastline.

Survey of Asterias larvae 2

Methods

Plankton sampling Plankton samples were washed into a specimen container and fixed with RNAlater (a commercial Zooplankton assemblages were sampled during molecular fixative). Three freeze‐dried brine August and September 2012. This corresponds shrimp were added to the samples at the time of with the period where Asterias larvae are most collection to assess sample preservation and abundant in the water column (Bruce et al. 1995, storage. Samples were stored at <4°C until they Bax and Dunstan 2004) and follows the peak in were transported, via courier, to SARDI’s spawning during July ‐ August (Byrne et al. diagnostic laboratory for analysis. 1997). Asterias larvae have previously been recorded from June to the end of October in Port Cross‐contamination between samples was Phillip Bay (Bax and Dunstan 2004). A survey minimised by towing the plankton net without conducted by DPI in PPB and WP on 7–8 the cod‐end for one minute at each site, prior to December 2011, following the outbreak at San sampling, to wash contents from net. Potential Remo, detected no Asterias DNA in the water cross‐contamination between field‐trips was column at this time. minimised by soaking the plankton net and cod‐ end in freshwater for two hours, rinsing the net Zooplankton was sampled at 31 locations and allowing to dry prior to use. There was no (Figure 1) from 1 August to 19 September (Table evidence of cross‐contamination between 1). Samples from PPB were collected on two samples or field‐trips (see results section). different occasions, at the start of the survey (1 August) and at the end of the survey (19 Fixed zooplankton samples were filtered in the September) to confirm the presence of Asterias laboratory onto qualitative filter paper (Filtech larvae in the water column during this period. filter paper grade 1803 (47 mm diameter, Cat No Asterias DNA was recorded at the beginning and 1803‐047)) and stored in 5 ml of RNAlater. DNA end of the survey (see also results). was extracted from filtered plankton samples using a modified variant of SARDI’s Root Zooplankton assemblages were sampled at two Disease Testing Service (RDTS) commercial locations in PPB at the beginning of the survey, DNA extraction method. DNA from the four locations in WP, four locations between plankton samples was then analysed using three PPB and WP, 10 locations off the coast of separate quantitative polymerase chain reaction Walkerville and Tidal River, seven locations in (qPCR) assays for a) evidence of PCR inhibition, Corner Inlet and off Port Welshpool, a single b) brine shrimp quality control for sample location in Tidal River estuary, two locations in quality and c) Asterias identification (see Bott et Andersons Inlet and a single location in PPB at al. 2010). Detection limits for the Asterias qPCR the end of the survey (Table 1). The location of assay are approximately 2 femtograms (fg)/ul of each site was recorded using GPS in the field. target DNA (i.e. 1 x 10‐15 g), substantially less Zooplankton was sampled using a 90 μm‐mesh than a single larva allowing for variation in plankton net (mouth diameter 0.48 m; length DNA extraction rates (Bax et al. 2006). 3.25 m, with cod‐end jar containing 90 μm‐mesh Results were plotted along the Victorian windows). Asterias eggs are approximately 105 coastline using ArcView GIS software. μm in diameter; larvae vary from 150 μm at the gastrula stage to 4.5 mm at the brachiolaria stage prior to settlement (Kashenko 2005). Hydrodynamic modelling Zooplankton was sampled at each site using a 5 The dispersal of Asterias larvae in coastal waters minute surface‐tow from a vessel moving at 2–3 between PPB and Cape Liptrap was examined knots: a distance of approximately 400 m using hydrodynamic and dispersion models – depending on tides and currents. This method with PPB as a larval source. The dispersal of samples surface waters to a depth of 0.5 m. In buoyant particles, simulating the behaviour of WP, Corner Inlet and Tidal River estuary Asterias larva in coastal waters, was modelled plankton samples were collected at high tide or using an 800 m grid, 8‐layer, 3D hydrodynamic on outgoing tides with the net towed into the and dispersion model (Black and Parry 1999, outgoing tide. Jenkins et al. 1999, Lee et al. 2012) that covered the region from Cape Patton to Cape Liptrap

Survey of Asterias larvae 3

and included the Port Phillip and Western Port embayments. The model was run using data for a typical year (2004) for the period July–October using observed forcing conditions (spring/neap tides, SW wind events, localised wave behaviour, rainfall) for this period. Hydrodynamic modelling generated information on the circulation patterns at hourly intervals and the dispersion model introduced particles into this flow field at a rate determined by expected larval release (pulse with outgoing tide from Port Phillip Bay) and survival (approximately 100 days) . The simulations examined the:  dispersal and distribution footprint of particles from PPB to Cape Liptrap, and  time it takes for particles to travel from Port Phillip Heads to Cape Liptrap. The latter was used to investigate if the time taken by particles to reach Cape Liptrap via passive dispersal was consistent with the larval duration of Asterias.

Survey of Asterias larvae 4

Table 1. Locations sampled in this survey including map codes used in figure 1, date and geographical position.

Sample Location Map code Date Latitude Longitude

1 Port Phillip Bay (spill ground) PPB 1 1/08/2012 ‐37.9836 144.8858 2Port Phillip Bay (Fawkner Beacon) PPB 2 1/08/2012 ‐37.9486 144.9276 3Western Port ‐ north Wport N 13/08/2012 ‐38.2730 145.3360 4Western Port ‐ east Wport E 13/08/2012 ‐38.3550 145.5090 5Western Port ‐ south Wport S 13/08/2012 ‐38.4500 145.3180 6Western Port ‐ west Wport W 13/08/2012 ‐38.3280 145.2330 7 PPB Heads BS 1 4/09/2012 ‐38.3161 145.6296 8Cape Schank BS 2 4/09/2012 ‐38.5151 144.8902 9 Flinders BS 3 4/09/2012 ‐38.5027 145.0671 10 Ventnor Channel (WP) BS 4 4/09/2012 ‐38.4359 145.1956 11 Cape Liptrap W1 11/09/2012 ‐38.9323 145.9218 12 Walkerville South W2 11/09/2012 ‐38.8852 146.0098 13 Waratah Bay W3 11/09/2012 ‐38.8396 146.0621 14 Off Shallow Inlet W4 11/09/2012 ‐38.8724 146.1561 15 2 km south Shallow Inlet W5 11/09/2012 ‐38.9251 146.2170 16 Adjacent Norman Is. NB1 11/09/2012 ‐39.0016 146.2621 17 Picnic Bay NB2 11/09/2012 ‐39.0294 146.2850 18 Norman Bay NB3 11/09/2012 ‐39.0414 146.3069 19 Oberon Bay NB4 11/09/2012 ‐39.0674 146.3216 20 2 km south Oberon Bay NB5 11/09/2012 ‐39.0894 146.3183 21 Corner Inlet C1 12/09/2012 ‐38.7680 146.2901 22 Corner Inlet C2 12/09/2012 ‐38.8098 146.3680 23 Corner Inlet C3 12/09/2012 ‐38.8200 146.3961 24 Barry Beach Terminal BB1 12/09/2012 ‐38.7172 146.3502 25 Barry Beach Terminal BB2 12/09/2012 ‐38.7142 146.3815

Survey 26 Port Welshpool PW1 12/09/2012 ‐38.7053 146.4615 27 Port Welshpool PW2 12/09/2012 ‐38.7165 146.5438 28 Tidal River estuary TR 13/09/2012 ‐39.0285 146.3187

of 29 Andersons Inlet AR1 18/09/2012 ‐38.6418 145.7233

Asterias 30 Andersons Inlet AR2 18/09/2012 ‐38.6396 145.7548 31 Port Phillip Bay (Fawkner Beacon) PPB 3 19/09/2012 ‐37.9485 144.9273 Geog co‐ords: GDA94

larvae

5

6 Survey

of

Asterias

larvae

Port Phillip Bay

Western Port

Port Welshpool

Figure 1. Map of sample locations (for location codes see Table 1).

Results

Plankton sampling collected off Norman Bay (Table 2). The plankton sample collected from the Tidal River The results of the genetic assays measuring the estuary contained only 94 pg of DNA suggesting amount of Asterias DNA in each sample are that only low densities of Asterias larvae were shown in Table 2. PCR results with the internal present. control show that some of the samples contained inhibitors that negatively affected PCR Major cross‐contamination between samples and amplification. This is not unusual for marine field‐trips appears unlikely. For example, no plankton samples (N. Bott, pers. comm.). Asterias DNA was detected in sample 3 taken in Accordingly, estimates of Asterias DNA were WP following the detection of 24,950 pg of DNA scaled to the level of inhibition (i.e. using scaling for the previous sample collected in PPB (see factors not shown) and this has been Table 2). Similarly, no Asterias DNA was incorporated into the final estimate of Asterias detected in samples collected in Corner Inlet DNA shown in Table 2. Brine shrimp sample following the detection of Asterias DNA in control results were within expected variation coastal waters off Wilsons Prom and Walkerville for plankton samples (N. Bott, pers. comm.). on the previous day (Table 2). It is impossible to completely eliminate cross‐contamination, Asterias DNA was detected in 20 of the 31 particularly between samples. However, there is samples collected in this survey (Table 2, Figure no evidence results were influenced by cross‐ 2). DNA was detected in all three samples contamination either between samples or field‐ collected in PPB, in three of four samples trips in this survey. collected in WP and in all four samples collected between PPB and WP. Asterias DNA was detected in all samples collected between Cape Hydrodynamic modelling Liptrap and Shallow Inlet (South Gippsland); The hydrodynamic and dispersal models and in three of the five samples collected indicate buoyant particles released from PPB are between Norman Island and Oberon Bay predominantly transported east and south‐east offshore of Tidal River. In addition, Asterias along the coastline to Cape Liptrap (Figure 3). DNA was recorded in samples collected from The greatest concentration of particles occurs Andersons Inlet and in Tidal River estuary. No offshore of Port Phillip Heads, the Mornington Asteria DNA was detected in samples collected Peninsula and . The model in Corner Inlet, off Barry Beach Marine Terminal simulation displays limited exchange between or in waters adjacent to Port Welshpool (Figure PPB and WP and lower particle concentrations 2). for the coastline between Cape Patterson and Cape Liptrap. The quantity of Asterias DNA detected in the survey varied by several orders of magnitude Hydrodynamic modelling of buoyant particles (Table 2) indicating high variation in the density predicted Asterias larvae are transported from of larvae collected in the samples. Asterias DNA Port Phillip Heads to Cape Liptrap via is measured in picograms (pg or 10‐12 g) of DNA prevailing easterly currents in approximately per sample. The highest amount of Asterias DNA 800 hours (33 days). This translates to a particle was recorded at Cape Schanck (Bass Strait) velocity of approximately 170 m/hour (i.e. 136 (25,418 pg) and the lowest amount of DNA (2 km/800 hours). At this rate the section of coast pg) was recorded at the eastern site in WP. between Cape Liptrap and Tidal River (approx. 45 km) can be traversed by buoyant particles in Samples collected offshore of Port Phillip Heads approximately 265 hours — a further 11 days. contained > 10,000 pg of Asterias DNA (Table 2, Figure 2), whereas samples collected from Cape Liptrap to Oberon Bay (with the exception of Waratah Bay where 1002 pg was recorded) contained <100 pg (Figure 2). Asterias DNA was detected in only two out of the five samples

Portland Marine Harbour Pest Surveys 7

8 Survey

Table 2. Genetic assay results showing the presence and quantity of Asterias DNA (pg/5 min tow) in each plankton sample.

of

Asterias Sample Location Map code Date Asterias (pg DNA)

1 Port Phillip Bay (spill ground) PPB 1 1/08/2012 738

larvae 2Port Phillip Bay (Fawkner Beacon) PPB 2 1/08/2012 24,950 3Western Port ‐ north Wport N 13/08/2012 0 4Western Port ‐ east Wport E 13/08/2012 2 5Western Port ‐ south Wport S 13/08/2012 283 6Western Port ‐ west Wport W 13/08/2012 425 7 PPB Heads BS 1 4/09/2012 10,320 8Cape Schank BS 2 4/09/2012 25,418 9 Flinders BS 3 4/09/2012 2,138 10 Ventnor Channel (WP) BS 4 4/09/2012 2,023 11 Cape Liptrap W1 11/09/2012 46 12 Walkerville South W2 11/09/2012 95 13 Waratah Bay W3 11/09/2012 1,002 14 Off Shallow Inlet W4 11/09/2012 23 15 2 km south Shallow Inlet W5 11/09/2012 39 16 Adjacent Norman Is. NB1 11/09/2012 0 17 Picnic Bay NB2 11/09/2012 17 18 Norman Bay NB3 11/09/2012 0 19 Oberon Bay NB4 11/09/2012 9 20 2 km south Oberon Bay NB5 11/09/2012 0 21 Corner Inlet C1 12/09/2012 0 22 Corner Inlet C2 12/09/2012 0 23 Corner Inlet C3 12/09/2012 0 24 Barry Beach Terminal BB1 12/09/2012 0 25 Barry Beach Terminal BB2 12/09/2012 0 26 Port Welshpool PW1 12/09/2012 0 27 Port Welshpool PW2 12/09/2012 0 28 Tidal River estuary TR 13/09/2012 94 29 Andersons Inlet AR1 18/09/2012 74 30 Andersons Inlet AR2 18/09/2012 351 31 Port Phillip Bay (Fawkner Beacon) PPB 3 19/09/2012 472 Positive detection in bold, UD: undetected

Survey

of

Asterias Figure 2. Bubble plot showing the quantity of Asterias DNA (pg/ 5 minute plankton tow) recorded at each location between PPB and Port Welshpool.

larvae

9

10 Survey

of

Asterias

larvae

Figure 3. 200 day simulation of continuous larval release (total of 96000 particles) from Port Phillip Bay between July and November shown as cumulative counts of visits per cell. The dispersion model provides an indication of the likelihood of Asterias larvae presence and key pathways.

Discussion

Distribution of Asterias larvae This study used a combination of plankton surveys and hydrodynamic modelling to examine the distribution of Asterias larvae in coastal waters between Port Phillip Bay (PPB) and Port Welshpool in eastern Victoria. The two approaches suggest Asterias larvae occur in coastal waters between PPB and Wilsons Promontory. First, Asterias larvae were detected in coastal waters between Cape Liptrap and Oberon Bay. Second, hydrodynamic modelling indicates larvae are likely to occur between Phillip Island and Cape Liptrap, despite the gap in sampling for this stretch of coastline (Figure 2). Moreover, hydrodynamic modelling found that buoyant particles exported from PPB could Figure 4. Directionally average currents for Bass Strait displaying residual velocity vectors reach Cape Liptrap (the geographical extent of the model) in approximately 33 days. Assuming (m/s). Source: SEA (south‐east Australia) a similar rate of transport, it was estimated that hydrodynamic model (Greer et al. 2008) larvae would reach the coast off Tidal River in a The amount of Asterias DNA recorded between further 11 days (i.e. 44 days in total). This is well Cape Liptrap and Oberon Bay was several within the estimated larval duration of 79–112 orders of magnitude lower than that recorded days for Asterias (Bruce et al. 1995). off Port Phillip Heads. This is consistent with a Larval densities declined with increasing dilution effect as larvae are transported further distance from PPB, which is consistent with PPB from their original source (see also Figure 3). High values of Asterias DNA recorded at being the primary source of larvae in this region and the outputs of the hydrodynamic/dispersion Waratah Bay may be due localised accumulation modelling (see Figure 3). The highest densities of larvae caused by a local gyre (circulation) effect (R. Lee, EPA pers. comm.). The absence of of Asterias DNA were recorded in PPB, at Port Philip Heads and off Cape Schanck. The high Asterias larvae for Corner Inlet, Barry Beach quantity of Asterias DNA off Port Phillip Heads marine terminal and Port Welshpool is also consistent with the influence of currents in and Cape Schanck suggest significant export of larvae into Bass Strait. determining the distribution of larvae. This is because currents flow primarily south across Hydrodynamic and dispersion modelling Bass Strait to the north coast of Tasmania, rather predicts larvae are transported predominately than around the tip of the Promontory and up eastwards along the coast by the prevailing into Corner Inlet (Figure 4). winter currents in this region (Figure 3). The Asterias larvae were also recorded in bays and currents in this region are influenced primarily by the prevailing wind direction (SW) and the inlets such as WP, Andersons Inlet and Tidal tides, and flow mainly from the west forming a River estuary. Hydrodynamic modelling does not support strong connectivity between PPB gyre rotating anticlockwise in Bass Strait and following the coastline towards Point Howe and WP (Figure 3); however, high DNA levels (Figure 4). were recorded at locations linking these two systems. Approximately 20 adult seastars were collected at San Remo (WP) between September and November 2011. This discovery raised

concerns about the presence of adult Asterias populations in WP. Unfortunately, the results of this survey are equivocal regarding the presence of adult

Survey of Asterias larvae 11

Asterias populations in WP. Asterias larvae were recorded along the coastline between PPB and present in WP during this survey, particularly in Wilsons Promontory during this time. the south and west of the bay and between Shoreham and Phillip Island, but this pattern is Role of larval dispersal in largely consistent with larvae arriving from PPB. Consequently, it is impossible to distinguish causing new outbreaks of larvae arriving from PPB from those that may Asterias? have originated from populations within WP. Only three adult populations have been The survey provides no definitive evidence of recorded outside of PPB in the 14 years since adult populations in WP . Asterias populations peaked in PPB: Andersons The presence of Asterias DNA in Andersons Inlet Inlet, San Remo and Tidal River. Each appears to and Tidal River estuary during September 2012 be a single, isolated recruitment event. is also most likely due to the intrusion of larvae However, the establishment of new populations into these systems from the open coast, rather of Asterias along the Victorian coastline is likely than a product of existing adult populations. In to be dependent on factors other than simply the the case of Andersons Inlet, Asterias have not presence of larvae in the water column. been detected in this system since the Successful recruitment requires the convergence eradication of the original outbreak in 2004– of a number of factors that influence the survival 2005, and in Tidal River a large flood event is of both larvae and juvenile seastars. Asterias believed to have removed/killed all remaining larvae need to be transported to suitable adults present (S. Howe pers. comm.). locations and habitat (e.g. inlets and bays), find Moreover, the low DNA levels recorded in the suitable substratum for settlement, and evade Tidal River estuary are similar to levels recorded predation and other forms of mortality during offshore between Norman Island and Oberon their early life. Conditions will also need to be Bay in this survey. favourable for the growth, reproduction and The presence of Asterias larvae in Bass Strait expansion of adult populations. conforms with the predictions of Dunstan and Little is known about the early life‐history of Bax (2007). Dunstan and Bax (2007) predicted larval and juvenile Asterias. Larvae need to Asterias larvae exported from PPB would diffuse evade predation and find sufficient food to across central Bass Strait to the Kent and King develop and grow. Both factors are likely to be Island groups and toward the northern coastline influenced by oceanographic and climatic of Tasmania. In contrast, the modelling in this processes that vary annually. These processes in study indicates that larvae are transported turn may influence the abundance of larvae predominantly to the east of PPB, past Phillip present in offshore waters. Mortality during this Island and along the South Gippsland coast. The phase is likely to be both exceptionally high and differences between this and earlier modelling highly variable (Bax and Dunstan 2004). The are likely to be due to recent improvements in vast majority of larvae are unlikely to find the oceanographic model for this coastline (e.g. suitable habitats for settlement, particularly Greer et al. 2008; R. Lee, EPA pers. comm.). The along the open coast. results of the hydrodynamic modelling in this study indicate the risk of larval dispersal by Successful recruitment from larvae may be a currents along the west coast to Cape Otway is relatively rare event, requiring the convergence low; however, no sampling of this coastline was of a range of factors that influence larval undertaken in this study. transport, survival and settlement. The rate of outbreaks suggests that such conditions may It is difficult to know how typical this overall only be infrequently suitable in Victorian waters pattern is because this is the only survey of its (i.e. on the basis of three known outbreaks in 14 kind. It is likely Asterias larvae have been years). However, future incursions along this present in coastal waters between PPB and coastline seem inevitable: given adult Wilsons Prom since Asterias populations reached populations appear to have successfully their initial peak in PPB in 1999/2000 (Parry et al. recruited in the past and that larvae will 2004); and PPB began to export high densities of continue to be exported from PPB over the larvae into Bass Strait. If this is a normal winter months. phenomenon this raises the question of why more outbreaks of Asterias have not been

Survey of Asterias larvae 12

Could the geographical pattern of Conclusions Asterias outbreaks in Victoria be  Asterias larvae were detected in coastal waters between PPB and Wilsons explained by other vectors? Promontory during August and September Ballast water is the principal vector implicated 2012. This finding is supported by in the introduction of Asterias to Australia, and hydrodynamic modelling of buoyant its subsequent translocation from south‐east particles simulating the behaviour of Tasmania to PPB (Ward et al. 1995, Bax and Asterias larvae exported from PPB Dunstan 2004). Ballast water provides a mechanism by which larvae can be transported  No Asterias larvae were detected in coastal beyond the range of natural larval dispersal (in waters east of Wilsons Prom (i.e. Corner terms of distance or prevailing currents). Inlet and Port Welshpool) and this is Although, legislation now minimizes the risk of consistent with the influence of the spread via ballast water for large commercial prevailing currents in Bass Strait and their shipping vessels, this still remains the main role in transporting Asterias larvae along the vector by which Asterias could be introduced to Victorian coast other ports within Australia (Bax and Dunstan  Asterias larvae were also detected in bays 2004). Ballast water also remains a significant and inlets such as WP, Andersons Inlet and vector by which Asterias could be spread Tidal River estuary. This is likely to be due between Victorian ports. to the intrusion of larvae into these systems If ballast water is a major vector involved in the from the open coast. Asterias larvae may also spread of Asterias along the Victoria coastline be present in Shallow Inlet, but this location then we would expect new outbreaks to occur at was not surveyed during this study locations unlikely to be reached by natural  The pattern of Asterias outbreaks at dispersal alone (i.e. the west coast of Victoria or Andersons Inlet, Western Port and Tidal further east along the Gippsland coast beyond River appears to be most consistent with Wilsons Promontory). Although, it is not natural range expansion by larval dispersal possible to dismiss the role of ballast water in (rather than other vectors); with PPB as the the spread of Asterias, the location of outbreaks source population appears entirely consistent with passive larval transport as the primary mode of dispersal,  Managers will need to be vigilant to prevent based on the plankton surveys and the spread of Asterias along the coastline hydrodynamic modelling undertaken in this between PPB and Wilsons Promontory. The study. presence of larvae along this coastline indicates further outbreaks are likely in Bax and Dunstan (2004) list a range of vectors Western Port, Andersons Inlet, around that could spread Asterias non‐larvae (juveniles Wilsons Promontory and also possibly and adults) around the coast of Australia. These Shallow Inlet. Protected embayments such include entanglement in nets/fishing gear, as Waratah Bay may also be susceptible, biofouling on vessel hulls and surfaces, and given the presence of larvae at relatively intentional introductions. In general Bax and high levels Dunstan (2004) considered the importance of these vectors low in comparison to ballast water.  Recommendations regarding further It is entirely conceivable that Asterias could be sampling: We recommend further sampling transported from PPB to WP by such activities, along the west coast of Victoria between particularly as there is high vessel traffic PPB and Cape Otway, and further east along between the two water bodies. However, as the East Gippsland coast to confirm the seastar are dioecious (sexes are separate) and outputs of the modelling and the pattern of fertilization occurs externally, the establishment larval dispersal described in this report. The of a founder population would require the hydrodynamic model indicates that larvae successful translocation of at least one are predominantly restricted to coastal individual of each sex (i.e. one individual would waters (see Figure 3), however, additional be insufficient to found a new population). sampling in offshore shipping lanes or in locations where ballast water exchanges occur may be also be informative in quantifying the distribution of Asterias larvae in Victorian waters. Sampling should

Survey of Asterias larvae 13

also be undertaken in Shallow Inlet, to confirm the presence/absence of larvae in this system.

Survey of Asterias larvae 14

Acknowledgements

Guy Werner, Brent Womersley, Paul Bozinis, Camille White and Matt Hoskins (Parks Victoria) provided technical support in the field. Thanks also to Brent Womersley for assistance in producing the GIS figures.

Survey of Asterias larvae 15

References

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